Abstract:

U-Pb dating and Hf isotope analysis of detrital zircons from Hetong formation and Gongdong formation of Danzhou group and Chang’ an formation of Nanhuan system were carried out by LA-ICP-MS to reveal the chronological records of sedimentary transformation between Danzhou period and Nanhuan glacial period in northern Guangxi. The analytical results show that the Hetong formation and Gongdong formation of Danzhou group have similar detrital zircon age pedigrees, and the U-Pb ages are concentrated in 720-1000 Ma, 1700-2300 Ma and 2400-2700 Ma. The detrital zircon ages of Chang’ an formation of Nanhuan system are concentrated in 650-720 Ma and 720-1000 Ma, which are obviously different from Danzhou group. Hetong formation and Gongdong formation of Danzhou group have similar Hf isotopic characteristics, with negative εHf(t) and the TDM2 values of most zircons are greater than 2400 Ma. However, the zircon Hf isotopic characteristics of Chang’ an formation of Nanhua system are different from Danzhou group, with mainly positive εHf(t) values and TDM2 values concentrated in 1000-1300 Ma and 1400-2200 Ma. The differences of U-Pb age spectrum and Hf isotope of detrital zircon, combined with the difference of zircon CL image and provenance, show that there is obvious sedimentary transformation between Nanhua system and Danzhou sedimentary strata.

Key words: detrital zircon, Hf isotope, sedimentary transformation, Danzhou group, Nanhua system, northern Guangxi